A magnetic device uses magnetic material arranged to shape and direct magnetic flux in a predetermined manner to achieve a desired electrical performance. The magnetic flux provides a medium for storing, transferring or releasing electromagnetic energy.
Magnetic devices most typically comprise a core having a predetermined volume and composed of a magnetic material (e.g., ferrite) having a magnetic permeability greater than that of a surrounding medium (e.g., air). A plurality of windings of a desired number of turns and carrying an electrical current surround, excite and are excited by the core (or legs thereof) Because the magnetic core has a relatively high permeability, magnetic flux produced by the windings is confined almost entirely to the core. The flux follows the path the core defines; flux density is essentially consistent over the uniform cross-sectional area of the core.
Magnetic devices are often used to suppress electromagnetic interference ("EMI"). When used in the suppression role, the efficiency with which a magnetic device stores and releases electrical power is not usually a concern. However, magnetic devices are also frequently employed to transmit, convert or condition electrical power (so-called "power magnetic devices"). When so employed (often in the environment of power supplies for electronic equipment), magnetic performance and efficiency become major concerns.
As with other types of electronic components, there is a trend in the design of power magnetic devices toward achieving increased power and volumetric density and lower device profile. To achieve higher power, the resistance of the power magnetic device must be reduced, typically by increasing the cross-sectional area of the electrical member forming the device windings. To increase the density of the power magnetic device, the windings are usually made relatively thin in the region constituting the core of the device to optimize the electrical member resistance.
Another problem associated with present-day power magnetic devices is the lack of planarity of the device terminations. Because of the need to optimize the winding thickness of the power magnetic device to provide the requisite number of turns while minimizing the winding resistance, the thickness of the electrical member forming each separate winding of the device is often varied. Variation in the winding thickness often results in a lack of planarity of the device terminations, an especially critical deficiency when the device is to be mounted onto a surface of a substrate, such as a printed circuit board ("PCB") or printed wiring board ("PWB").
A surface-mountable power magnetic device is disclosed in U.S. Pat. application Ser. No. 08/434,485, filed on May 4, 1995, to Pitzele, et al., entitled "Power Magnetic Device Employing a Leadless Connection to a Printed Circuit Board and Method of Manufacture Thereof," commonly assigned with the present invention and incorporated herein by reference. The surface-mountable power magnetic device includes a multi-layer circuit containing a plurality of windings disposed in layers and a magnetic core mounted proximate the plurality of windings. The magnetic core is adapted to impart a desired magnetic property to the plurality of windings. The plurality of windings and the magnetic core are substantially free of a surrounding molding material to allow the magnetic device to assume a smaller overall device volume. The surface-mountable power magnetic device also includes an improved termination or lead structure that attains electrical isolation and thermal conductivity without requiring a molding compound.
Pitzele, et al., further discloses a manual method of manufacturing the power magnetic device wherein, after the multi-layer flex circuit is prepared, an epoxy adhesive is applied to a first core-half of the magnetic core and the first core-half is joined to a second core-half. The magnetic core-halves are twisted to ring the adhesive and create a very minute interfacial bond line between the first and second core-halves. The magnetic cores are then held together using mechanical compression (e.g., with a clip or clamp) while the epoxy adhesive between the core halves cures.
While the method of Pitzele, et al., provides a reliable process of manufacturing a power magnetic device, innovative pick and place assembly techniques may be applied with respect to core assembly to reduce the cost and increase the manufacturing yield for such power magnetic devices. In view of the compactness of the present power magnetic devices and- the competitive pressures on price, an increase in manufacturing efficiency is highly desirable.
Accordingly, what is needed in the art is a method of manufacturing power magnetic devices having a relatively high power density and small footprint that addresses the need for automation and reliability in the production of such power magnetic devices.